Update volume sample to use audio worklet

fixes #1509

Author: fippo

src/content/getusermedia/volume/js/soundmeter.js

@@ -18,32 +18,22 @@ function SoundMeter(context) {
   this.instant = 0.0;
   this.slow = 0.0;
   this.clip = 0.0;
-  this.script = context.createScriptProcessor(2048, 1, 1);
-  const that = this;
-  this.script.onaudioprocess = function(event) {
-    const input = event.inputBuffer.getChannelData(0);
-    let i;
-    let sum = 0.0;
-    let clipcount = 0;
-    for (i = 0; i < input.length; ++i) {
-      sum += input[i] * input[i];
-      if (Math.abs(input[i]) > 0.99) {
-        clipcount += 1;
-      }
-    }
-    that.instant = Math.sqrt(sum / input.length);
-    that.slow = 0.95 * that.slow + 0.05 * that.instant;
-    that.clip = clipcount / input.length;
-  };
+  this.node = null;
 }
 
-SoundMeter.prototype.connectToSource = function(stream, callback) {
+SoundMeter.prototype.connectToSource = async function(stream, callback) {
   console.log('SoundMeter connecting');
   try {
+    await this.context.audioWorklet.addModule('js/volume-meter-processor.js');
     this.mic = this.context.createMediaStreamSource(stream);
-    this.mic.connect(this.script);
-    // necessary to make sample run, but should not be.
-    this.script.connect(this.context.destination);
+    this.node = new AudioWorkletNode(this.context, 'volume-meter-processor');
+    this.node.port.onmessage = (event) => {
+      const {instant, clip} = event.data;
+      this.instant = instant;
+      this.clip = clip;
+      this.slow = 0.95 * this.slow + 0.05 * this.instant;
+    };
+    this.mic.connect(this.node);
     if (typeof callback !== 'undefined') {
       callback(null);
     }
@@ -58,5 +48,5 @@ SoundMeter.prototype.connectToSource = function(stream, callback) {
 SoundMeter.prototype.stop = function() {
   console.log('SoundMeter stopping');
   this.mic.disconnect();
-  this.script.disconnect();
+  this.node.disconnect();
 };

src/content/getusermedia/volume/js/volume-meter-processor.js

@@ -0,0 +1,40 @@
+/*
+ *  Copyright (c) 2025 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree.
+ */
+
+'use strict';
+
+// This class is used to compute the volume of the input audio stream.
+class VolumeMeterProcessor extends AudioWorkletProcessor {
+  constructor() {
+    super();
+    this._lastUpdate = Date.now();
+  }
+  process(inputs) {
+    // This example only supports mono channel.
+    const input = inputs[0][0];
+    if (!input) {
+      return true;
+    }
+    let sum = 0.0;
+    let clipcount = 0;
+    for (let i = 0; i < input.length; ++i) {
+      sum += input[i] * input[i];
+      if (Math.abs(input[i]) > 0.99) {
+        clipcount += 1;
+      }
+    }
+    const instant = Math.sqrt(sum / input.length);
+    this.port.postMessage({
+      instant: instant,
+      clip: clipcount / input.length,
+    });
+    return true;
+  }
+}
+
+registerProcessor('volume-meter-processor', VolumeMeterProcessor);